Color filter panel and liquid crystal display including the same

ABSTRACT

An LCD comprising a first substrate having an inner surface and an outer surface; a green color filter formed on the outer surface of the first substrate; red, green, and blue color filters formed on the inner surface of the first substrate; a second substrate facing the first substrate and having an inner surface and an outer surface; a pixel electrode formed on the inner surface of the second substrate; a common electrode formed on the inner surface of one of the first and second substrates; and a liquid crystal layer disposed between the first substrate and the second substrate is provided. By this structure, a green light having color purity is produced. The manufacturing method of an LCD is simplified by replacing the black matrix with the overlapped color filters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/917,186, filed Aug. 10, 2004, which claims priority to KoreanApplication 2003-72092, filed Oct. 16, 2003, the disclosures of whichare incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to liquid crystal displays (LCDs), and indetail, to a method for improving display quality and viewing angle ofLCDs.

(b) Description of the Related Art

An LCD includes two panels provided with field-generating electrodes,and a liquid crystal (LC) layer interposed therebetween. The LCDdisplays images by applying voltages to the field-generating electrodesto generate an electric field in the LC layer, which determinesorientations of LC molecules in the LC layer to adjust polarization ofincident light.

In an LCD, usually, red, green, and blue color filters are sequentiallydisposed. Color images are displayed by controlling intensity of lightwhich passes through the color filters.

However, there are limitations in displaying full colors by using threecolor filters.

Recently, as LCDs have been gaining popularity as multi-media displays,the need for good color reproducibility has increased. Especially, whenan LCD is used as a television, good color reproducibility is extremelyimportant.

When color reproducibility is discussed, the green color is important.The green color of the National Television Standards Committee (NTSC) ismarked at x=0.21, y=0.70 on color coordinates of the InternationalCommission of Illumination (CIE). However, the green light from theconventional green color filter of an LCD television having a thicknessof 1.9 μm is marked at x=0.275, y=0.60 on the CIE color coordinatesystem.

When the conventional green color filter is used, the colorreproducibility reaches only up to 72% of natural color. If one wishesto make a green color filter producing green color of NTSC which allowscolor reproducibility of 80% to 100%, one of the following two methodsmay be used. The first is increasing the dispersion density of pigmentsin the color filter, and the second is increasing the thickness of thecolor filter. However, when the dispersion density of pigments in thecolor filter is increased, stability of the photoresist of the colorfilter is degraded. When the thickness of the color filter is increased,the color filter needs to have a thickness of about 7.6 μm, which isfour times thicker than that of the normal color filter. This causesdifficulty in forming the color filter.

SUMMARY OF THE INVENTION

To solve such a problem, the present invention comprises a color filterpanel having green color filters on both sides thereof.

In more detail, a liquid crystal display comprising a first substratehaving an inner surface and an outer surface; a green color filterformed on the outer surface of the first substrate; red, green, and bluecolor filters formed on the inner surface of the first substrate; asecond substrate facing the first substrate and having an inner surfaceand an outer surface; a pixel electrode formed on the inner surface ofthe second substrate; a common electrode formed on the inner surface ofone of the first and second substrates; and a liquid crystal layerdisposed between the first substrate and the second substrate isprovided.

The green color filter formed on the outer surface of the firstsubstrate may be disposed on the whole display area except at red andblue pixel areas, the green and blue color filters formed on the innersurface of the first substrate are respectively disposed on green andblue pixel areas, and the red color filter formed on the inner surfaceof the first substrate is disposed on the whole display area except atthe green and blue pixel areas.

The green color formed on the outer surface of the first substrate maybe at least 2.5 times the thickness of the green color filter formed onthe inner surface of the first substrate.

A color filter panel comprising a transparent insulating substratehaving two surfaces; a green color filter formed on a first surface ofthe insulating substrate; and red, green, and blue color filters formedon a second surface of the insulating substrate, wherein the green colorfilter formed on the first surface is removed in predetermined areas toexpose part of the first surface of the insulating substrate, the redcolor filter formed on the second surface is disposed on the area exceptat the areas that the green and blue color filters are disposed, and thered and blue color filters formed on the second surface are seen throughthe predetermined areas exposing the first surface of the insulatingsubstrate is provided.

The color filter panel may further include a transparent electrodeformed on the red, green, and blue color filters. The thickness of thegreen color filter formed on the first surface may be 2.5 times thethickness of the green color filter formed on the second surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will become moreapparent by describing preferred embodiments thereof in detail withreference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a liquid crystal display (LCD) accordingto an exemplary embodiment of the present invention;

FIG. 2 is a layout view of the color filter panel of the LCD accordingto the exemplary embodiment of the present invention shown from the topside;

FIG. 3 is a layout view of the color filter panel of the LCD accordingto the exemplary embodiment of the present invention shown from thebottom side;

FIG. 4 shows spectrum graphs of a light passing through a 1.9 μm greencolor filter and a light passing through a green color filter accordingto an exemplary embodiment of the present invention; and

FIG. 5 shows spectrum graphs of three kinds of light respectivelypassing through three kinds of color filters according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

In the drawings, the thickness of layers, films, and regions areexaggerated for clarity. Like numerals refer to like elementsthroughout. It will be understood that when an element such as a layer,film, region, or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent.

Now, liquid crystal displays according to embodiments of the presentinvention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view of a liquid crystal display (LCD) accordingto an exemplary embodiment of the present invention. FIG. 2 is a layoutview of the color filter panel of the LCD according to the exemplaryembodiment of the present invention shown from the top side. FIG. 3 is alayout view of the color filter panel of the LCD according to theexemplary embodiment of the present invention shown from the bottomside.

An LCD according to an exemplary embodiment includes a thin filmtransistor (TFT) array panel 100, a color filter panel 200 facing theTFT array panel 100, a liquid crystal layer disposed between the twopanels 100 and 200, a pair of compensation films 11 and 21 respectivelydisposed on the outside of the two panels 100 and 200, and a pair ofpolarizing films 12 and 22 respectively disposed on outside of the twocompensation films 11 and 12.

The TFT array panel 100 will now be described in detail.

A plurality of pixel electrodes 190 made of indium tin oxide (ITO) orindium zinc oxide (IZO) are formed on a transparent substrate such asglass. Each pixel electrode 190 is connected to a TFT which is aswitching element and is applied an image signal voltage through theTFT. Here, the TFT has a gate electrode connected to a gate line (notillustrated) transmitting scanning signals, a source electrode connectedto a data line (not illustrated) transmitting image signals, and a drainelectrode connected to the pixel electrode 190 that switches the imagesignals according to the scanning signals.

For a reflective LCD, the pixel electrode 190 is formed of a reflectivemetal instead of a transparent material, and the lower polarizing film12 and the lower compensation film 11 are omitted.

Next, the color filter panel 200 will be described in detail.

Red, green, and blue color filters 230R, 230G, and 230B and a commonelectrode 270 made of a transparent conductive material such as indiumtin oxide (ITO) or indium zinc oxide (IZO) are formed on the lowersurface of an upper substrate 210 made of a transparent insulatingmaterial such as glass.

Here, the green color filter 230G and the blue color filter 230B arerespectively formed on the corresponding pixel areas. The red colorfilter 230R is formed on the whole display area except at the areas ofthe green and blue color filters 230G and 230B, but including the redpixel area.

The thickness of the color filters 230R, 230G, and 230B are about 1.9μm.

A green color filter 230G is formed on the upper surface of the uppersubstrate 210.

The green color filter 230G formed on the upper surface of the uppersubstrate 210 is disposed on the whole area of the display area exceptat the areas of the red and blue pixels.

Here, the display area means an area to display images in an LCD. Thegreen color filter 230G formed on the upper surface of the uppersubstrate 210 has a thickness of about 5.7 μm.

The thickness of the color filters formed on the lower and uppersurfaces of the upper substrate 210 may be modified according to theirproperties. However, under any circumstances, the thickness ratio of thegreen color filter on the lower surface to that on the upper surface ispreferably over 1:2.5.

As described above, when green color filter 230G is formed on the uppersurface of the upper substrate 210, and the red, green, and blue colorfilters 230R, 230G, and 230B are formed on the lower surface of theupper substrate 210, a red light and a blue light are respectivelyproduced by the red color filter 230R and the blue color filter 230Bhaving thickness of about 1.9 μm in the red and blue pixels, and a greenlight having high color purity is produced by the green color filters230G having a total thickness of about 7.6 μm in the green pixel. Thered color filter 230R and the green color filter 230G overlap each otherto block almost all of the light in the areas between the pixel areasand the area around the display area. The overlapped red and green colorfilters 230R and 230G play a role of a black matrix.

The lower polarizing film 12 and the upper polarizing film 22 arepreferably disposed to make their polarizing axes perpendicular to eachother. Under such polarizing films disposition, the LCD shows a normallyblack mode such that black is displayed when there is no electric fieldin the liquid crystal layer

According to the present invention, the green color filter 230G can havesufficient thickness since the green color filters 230G are formed onboth side of the color filter panels 200. Such a green color filterhaving sufficient thickness can produce a green light having high colorpurity.

FIG. 4 shows spectrum graphs of a light passing through a 1.9 μm greencolor filter and a light passing through a green color filter accordingto an exemplary embodiment of the present invention.

In FIG. 4, curve A represents a spectrum graph of a light passingthrough 1.9 μm green color filter, and curve B represents a spectrumgraph of a light passing through a green color filter according to anexemplary embodiment of the present invention.

As shown in FIG. 4, the spectrum of the green light produced by thegreen color filter according to the present invention is distributed ina narrower wavelength range than that of the green light produced by aconventional green color filter having a thickness of 1.9 μm.

The overlapped red and green color filters 230R and 230G replace theblack matrix in the exemplary embodiment of the present invention. Thereason why the overlapped red and green color filters 230R and 230G canplay a role of a black matrix will be described with reference to FIG.5.

FIG. 5 shows spectrum graphs of three kinds of lights respectivelypassing through three kinds of color filters according to an exemplaryembodiment of the present invention.

As shown in FIG. 5, the green color filter 230G of the exemplary LCDaccording to the present invention is a band pass filter of wavelengthsranging from 495˜580 nm, and the red color filter 230R is a high passfilter of wavelengths of 580 nm or longer. According, when a white lightpasses through both the green and red color filters 230G and 230R, allthe light will be blocked by the color filters 230G and 230G to displayblack.

As described above, in the present invention, a green light having highcolor purity is produced by forming the green color filters on bothsides of the upper substrate 210. The manufacturing method of an LCD issimplified by replacing the black matrix with the overlapped colorfilters 230R and 230G.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

1. A liquid crystal display comprising: a first substrate having aninner surface and an outer surface; a green color filter formed on theouter surface of the first substrate; red, green, and blue color filtersformed on the inner surface of the first substrate; a second substratefacing the first substrate and having an inner surface and an outersurface; a pixel electrode formed on the inner surface of the secondsubstrate; a common electrode formed on the inner surface of one of thefirst and second substrates; and a liquid crystal layer disposed betweenthe first substrate and the second substrate.
 2. The liquid crystaldisplay of claim 1, wherein the green color filter formed on the outersurface of the first substrate is disposed on all the display areaexcept at red and blue pixel areas, the green and blue color filtersformed on the inner surface of the first substrate are respectivelydisposed on green and blue pixel areas, and the red color filter formedon the inner surface of the first substrate is disposed on all thedisplay area except at the green and blue pixel areas.
 3. The liquidcrystal display of claim 2, wherein the green color filter formed on theouter surface of the first substrate is at least 2.5 times thicker thanthe green color filter formed on the inner surface of the firstsubstrate.
 4. A color filter panel comprising: a transparent insulatingsubstrate having two surfaces; a green color filter formed on a firstsubstrate of the insulating substrate; and red, green, and blue colorfilters formed on a second surface of the insulating substrate, whereinthe green color filter formed on the first surface is removed atpredetermined areas to expose the first surface of the insulatingsubstrate, the red color filter formed on the second surface is disposedeverywhere except at the areas where the green and blue color filtersare disposed, and the red and blue color filters formed on the secondsurface are seen through the predetermined areas exposing the firstsurface of the insulating substrate.
 5. The color filter panel of claim4, further including a transparent electrode formed on the red, green,and blue color filters.
 6. The color filter panel of claim 4, whereinthe thickness of the green color filter formed on the first surface is2.5 times the thickness of the green color filter formed on the secondsurface.